1. Field of the Invention
This invention generally relates to UPnP communications and, more particularly, to a system and method for supplying a byebye notification for devices that fail to advertise when they leave a UPnP network.
2. Description of the Related Art
UPnP is a technology used for device and service discovery in a home network. UPnP takes a decentralized approach to service discovery. A networked device announces that it is present, when it is connected or becomes active. When initially connected, a search capacity for other networked devices and UPnP services is provided. However, a networked device is typically expected to search only when first connected, and otherwise depends on advertisements to become aware of new devices being networked, or known devices leaving the network. That is, networked devices are expected to announce when they enter the network (Notify with ssdp:alive) and leave the network or become unavailable (Notify with ssdp:byebye). However, it is possible for a device to be removed from the network without making a ssdp:byebye announcement. For example, when a device is powered off without going through a shutdown process. In this case the previous advertisement will eventually expire, because there is no re-advertisement by the removed device. The duration, for which an advertisement is valid, is transmitted with the advertisement, and is known as CACHE-CONTROL. UPnP specifies that this duration should be greater than 30 minutes (1800 seconds).
In wireless networks it is very common for a device to become disassociated from the network, if it moves outside the range of the access point (AP). In this case, the device is removed from the network without the ssdp:byebye message being sent. All other networked devices assume that the removed device is still available, and may attempt to access its services. The assumption that the removed device is available may result in a bad user experience. It is desirable to provide the byebye message if the removed device moves out of range of the AP and does not send the message. Even in a wired network, a similar problem may result when a device is powered down abruptly or the network cable is disconnected.
It would be advantageous if byebye advertisement could be supplied for a device that is removed from a network, if that device fails to make the advertisement itself.